Protective coatings for improved tarnish resistance in metal foils

ABSTRACT

In one embodiment, the present invention relates to a composite article, comprising a metal foil having a first side and a second side; a protective film of at least one inert silane, titanate or zirconate overlying the first side of the metal foil; and a metal sheet having a first side and a second side, the first side overlying the protective film. In another embodiment, the present invention relates to a method of increasing tarnish resistance of metal foil comprising contacting the metal foil with an inert silane, titanate or zirconate compound to form a protective film having a thickness from about 0.001 microns to about 1 micron on a surface of the metal foil; and attaching the foil to a metal sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a division of U.S. application Ser. No.09/714,811, filed Nov. 15, 2000, now U.S. Pat. No. 6,537,675, which is acontinuation-in-part of U.S. application. Ser. No. 09/211,283, filedDec. 14, 1998, and entitled “COATINGS FOR IMPROVED RESIN DUSTRESISTANCE”, now U.S. Pat. No. 6,299,721.

TECHNICAL FIELD

The present invention relates to a composite article and a method fortreating metal foil to prevent or avoid tarnish of the surface of themetal foil. In particular, the present invention relates to a method offorming the composite article including treating the metal foil with aninert silane, titanate or zirconate compound to form a protective filmwhich improves the metal foil's resistance to tarnish when the metalfoil is attached or held adjacent to a metal sheet comprising adifferent metal.

BACKGROUND OF THE INVENTION

Copper clad laminates are the basic component of the printed circuitboards used in the electronics industry. In the most common processes, acopper foil is bonded to a prepreg of resin, such as epoxy resin, whichhas been impregnated into fiberglass by heat and pressure. The copperfoil surface that is pressed against the prepreg is typically an unevenor profiled surface with some kind of additional bonding treatmentapplied to insure that the laminate remains together under normalprocessing conditions.

The opposing foil surface (the surface not bonded to the prepreg) istypically a smooth surface with various treatments that are aimed atpreventing oxidation of the foil and allowing solder wettability andadequate photoresist adhesion. Such coatings may include metals such aszinc or chromium or alloys thereof. A number of such metal treatmentsare disclosed in U.S. Pat. No. 5,908,544, which is incorporated hereinby reference for its teachings with respect to such coatings.

The opposing foil surface is often placed against or attached to a metalsheet comprised of a metal other than the metal foil. Thus, the metalfoil may be made of a first metal, such as copper, and the metal sheetmay be made of a second metal, such as aluminum. Metal foils aretypically very thin and need to be protected from indenting, scratching,bending and folding during shipping, storage and handling prior to andduring the lamination of the foil to prepregs. Metal sheets, of a metalwhich is less expensive and may be discardable, are commonly used forthe purpose of providing such protection. In addition, such metal sheetscan provide for distribution of heat and pressure in laminationprocesses, and act as a separator-release plate, or separator sheet,during the lamination of metal foil-prepreg laminates into books, fromwhich PCBs are formed. The metal sheets may be made of any metal, suchas stainless steel or aluminum. Aluminum is widely used in the industrytoday, due to the facts that it is relatively inexpensive and it can berecycled, which facilitates discarding of the metal sheet subsequent toits use. Such metal sheets, and methods of using the sheets with metalfoils such as copper foils, are disclosed in U.S. Pat. Nos. 4,875,283and 5,153,050, and the progeny of each of these patents. The disclosuresof both U.S. Pat. Nos. 4,875,283 and 5,153,050 are incorporated hereinby reference for their teachings of the use of metal sheets andseparator sheets with metal foils.

As disclosed in detail in U.S. Pat. No. 4,875,283, the method thereofmakes laminated printed circuit boards of the type having outerconductive metallic layers and at least one inner dielectric layercontaining heat curable resin. The metal sheets (referred to therein as“separator-release sheets”) are formed of aluminum and are coated onboth sides with a polymeric resin release material in order to avoid orprevent adhesion between the conductive metal layer, which is generallya metal foil, in particular a copper foil, and the metal sheet. Inaddition to aluminum as the metal of the metal sheets, other metals maybe used for this purpose.

The process of making the laminated printed circuit boards disclosed inU.S. Pat. No. 4,875,283 involves assembling a multi-layer book ofcircuit boards, one on top of another, in a press lay-up. In the processdescribed in U.S. Pat. No. 4,875,283, a metal sheet is placed inengagement with each outer metallic layer of the board, and the laid-upbook is subjected to heat and pressure to cure the resin. Next, at leastone of the cured boards is separated from the book with the metalseparator sheet remaining in engagement with the outer metallic layer ofthe separated board. Subsequently, the board may be drilled with themetal sheet attached to form, e.g., conductor lead holes in the board.Thereafter, the metal sheet is removed. The metal sheets may serve toprevent the resin from contaminating adjacent boards in the curingprocess, and also serve as drill entry and drill backup material in thedrilling process, as well as serving as separator sheets in thelamination process.

As described in U.S. Pat. No. 4,875,283, the metal sheets provideprotection to the metal foil during the lamination process. In addition,the metal sheet may be used to provide such protection prior to suchlamination, such as during processing and handling.

When the metal sheet is attached to a metal foil, such as a copper foil,for use other than the immediate lamination steps described in U.S. Pat.No. 4,875,283, the metal foil is attached with an adhesive, as describedin U.S. Pat. No. 5,153,050. When the metal foil is copper foil, themetal sheet is aluminum and a single copper foil is attached to one sideof the aluminum sheet, the article is referred to as “CA.” When themetal foil is copper foil, the metal sheet is aluminum and a copper foilis attached to both sides of the aluminum sheet, the article is referredto as “CAC.”

A problem which has been encountered in the use of metal sheets such asthose of U.S. Pat. Nos. 4,875,283 and 5,153,050 with metal foils istarnishing, oxidation and/or corrosion of the surface of the metal foilfacing the metal sheet, which problem types are generally referred toherein simply as “tarnish” or “tarnishing.”

Thus, a need exists in the art for metal foils which resist theformation of tarnish, oxidation and/or corrosion when in contact withmetal sheets.

SUMMARY OF THE INVENTION

In one embodiment, the present invention relates to a composite article,comprising a metal foil having a first side and a second side; aprotective film of at least one inert silane, titanate or zirconateoverlying the first side of the metal foil; and a metal sheet having afirst side and a second side, the first side overlying the protectivefilm.

In another embodiment, the composite article further includes a prepreglaminated to the second side of the metal foil.

In one embodiment, the metal foil comprises copper. In one embodiment,the metal sheet comprises aluminum. In one embodiment, the protectivefilm is formed from an inert silane. In one embodiment, the inert silaneis propyltrimethoxysilane.

In another embodiment, the composite article further includes a secondmetal foil having a first side and a second side; a protective filmformed of at least one inert silane, titanate or zirconate overlying thefirst side of the second metal foil; and the second side of the metalsheet overlying the protective film on the second metal foil.

In one embodiment, the first and second metal foils each include a firstportion which is adjacent to the metal sheet and a second portion whichextends beyond a periphery of the metal sheet. In one embodiment, thesecond portions of the first and second metal foils are attached to eachother. In one embodiment, the first portions of the first and secondmetal foils are adjacent to, but are not attached to, the metal sheet.

In one embodiment, the present invention relates to an article for usein printed circuit board manufacture, comprising:

a metal sheet of a first metal;

a metal foil of a second metal different from the first metal, a firstside of the metal foil attached to a side of the metal sheet, the firstside of the metal foil having bonded thereto a protective film having athickness from about 0.001 microns to about 1 micron on a surface of themetal foil, the protective film formed of an inert silane, titanate orzirconate compound.

In another embodiment, the present invention further relates to anarticle for use in printed circuit board manufacture, comprising:

a metal sheet of a first metal, the metal sheet having a length andwidth;

a pair of metal foils of a second metal different from the first metal,a first side of the metal foil adjacent a side of the metal sheet, thefirst side of the metal foil having bonded thereto a protective filmhaving a thickness from about 0.001 microns to about 1 micron on asurface of the metal foil, the protective film formed of an inertsilane, titanate or zirconate compound,

wherein each of the pair of metal foils have a length and width greaterthan the length and width of the metal sheet and the pair of metal foilsare adhered to each other.

In one embodiment, the present invention relates to a method ofincreasing tarnish resistance of a metal foil of a first metal attachedto a metal sheet of a second metal, comprising:

contacting at least one side of the metal foil with an inert silane,titanate or zirconate compound to form a protective film having athickness from about 0.001 microns to about 1 micron on a surface of themetal foil; and

attaching a side of the metal foil having the protective film to themetal sheet.

In another embodiment, the present invention relates to a method oftreating metal foil comprising a method of increasing tarnish resistanceof metal foil comprising:

contacting the metal foil with an inert silane compound to form aprotective film having a thickness from about 0.001 microns to about 1micron on a surface of the metal foil.

In another embodiment, the present invention relates to a method oftreating metal foil comprising:

contacting a first side of the metal foil with a hydrocarbylsilanesolution to form a protective film on a surface of the metal foil, thehydrocarbylsilane solution comprising from about 0.01% to about 10% v/vof a hydrocarbylsilane;

attaching the first side to a metal sheet of a metal other than that ofthe metal foil; and

laminating a second side of the metal foil to a prepreg.

In yet another embodiment, the present invention relates to a method oftreating copper foil comprising a method of treating copper foilcomprising:

contacting the copper foil with a solution comprising from about 0.05%to about 5% v/v of an alkyl silane;

attaching a first side of the copper foil to an aluminum sheet; and

laminating the copper foil to an epoxy resin material.

With the present invention, it is possible to provide metal foil whichexhibits high tarnish resistance when attached to a metal sheet made ofa metal different from that of the metal foil. In particular, thepresent invention provides a protective coating for application to ametal foil surface that prevents tarnish from forming, particularly onthe side of the metal foil which is adjacent a metal sheet and which isnot adjacent a prepreg. Thus, a clean, tarnish-free metal foil surfaceremains after the metal foil has been attached to or held adjacent to,used with, e.g., in lamination, and subsequently detached from, a metalsheet made of a different metal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a single metal foil,treated with a protective film of an inert silane, attached to a metalsheet, in accordance with the present invention.

FIG. 2 is a schematic cross-sectional view of two metal foils, eachtreated with a protective film of an inert silane, attached to a metalsheet, in accordance with the present invention.

FIG. 3 is a schematic plan view of a partially peeled-back metal foil,treated with a protective film of an inert silane, attached to a metalsheet, in accordance with the present invention.

FIG. 4 is a schematic cross-sectional view of two metal foils, eachtreated with a protective film of an inert silane, attached to a metalsheet, in which the metal foils are larger than the metal sheet and areattached to each other, in accordance with the present invention.

FIG. 5 is a schematic plan view of a partially peeled-back metal foil,treated with a protective film of an inert silane, attached to a metalsheet, in which the metal foil and a second metal foil are larger thanthe metal sheet and are attached to each other, in accordance with thepresent invention.

DESCRIPTION OF THE INVENTION

The present invention relates to treating metal foil by contacting thesurface of a metal foil with an inert silane, titanate or zirconatecompound to protect the metal foil by imparting tarnish resistance tothe metal foil when the metal foil is attached to a metal sheet of adifferent metal. Such a foil/metal sheet article may be referred to as“FS”; when two metal foils are attached to a single metal sheet, thearticle may be referred to as “FSF”; and when two metal foils sandwich ametal sheet and the foils are attached to each other but not to themetal sheet, the article may be referred to as “F-to-F.” When the “F”and “S” are, for example, a copper foil and an aluminum sheet, thearticle conveniently may be referred to as “CA”, as “CAC” or as“C-to-C.”

In one embodiment, the treatment by contacting the metal foil with aninert silane, titanate or zirconate provides increased tarnishresistance to the metal foil when the metal foil is attached to a metalsheet and subsequently laminated to, e.g., laminating materials such asprepreg materials. In one embodiment, inert silane compounds are usedfor the treatment. In one embodiment, the side of the metal foil whichwill face the metal sheet is treated (the side which will not beadjacent the prepreg). In one embodiment, both sides of the metal foilare so treated.

As used herein, the terms “tarnish” or “tarnishing” encompass formationof tarnish, oxidation and/or corrosion on the surface of the metal foil.

As used herein, the term “tarnish-resistant” means that the metal foilresists formation of tarnish during the period of time it is attached orheld adjacent to the metal sheet, including, e.g., during storage,during lamination of the metal foil to prepregs, and during laminationof multiple laminates of metal foil and prepreg into multilayer PCBsknown as “books.”

As used herein, the term “protective film” refers to a film formed froman inert silane, titanate or zirconate compound in accordance with thepresent invention. The protective film disclosed herein provides tarnishresistance to a metal foil to which the protective film is applied.

As used herein, the term “overlies” and cognate terms such as“overlying” and the like, when referring to the relationship of one or afirst layer relative to another or a second layer, refers to the factthat the first layer partially or completely lies over the second layer.The first layer overlying the second layer may or may not be in contactwith the second layer. For example, one or more additional layers may bepositioned between the first layer and the second layer. The term“underlies” and cognate terms such as “underlying” and the like havesimilar meanings except that the first layer partially or completelylies under, rather than over, the second layer.

As used herein, an inert silane, titanate or zirconate compound is onewhich includes a polar, reactive portion and an essentially inert,non-reactive hydrophobic portion. The reactive portion of the inertsilane, titanate or zirconate compound, upon application to a metalsubstrate bonds to or combines with the metal substrate, and leaves theinert, non-polar hydrophobic portion of the molecule exposed. Thus, theinert silane, titanate or zirconate compound includes a polar, reactiveportion which reacts and/or combines with the surface of the metal foiland thereby provides an attachment to the foil for the inert, non-polarhydrophobic portion which faces away from the metal foil.

As used herein, the term “metal sheet” refers to a sheet of metal whichmay be attached to, in contact with, adjacent to or otherwise associatedwith one or more metal foils. The metal sheet may act as a support orcarrier for the metal foil, and, during a lamination step, may also actas a separator sheet or as a separator/release sheet, as those terms areknown and used in the metal foil lamination arts. The metal sheetgenerally may be a metal which is different from a metal of theassociated metal foil.

Tarnish typically appears after lamination of the metal foil tolaminating materials, such as epoxy resin materials, polyimide resinmaterials, and polyester resin materials. However, tarnish may appearafter extended storage, shipping or any exposure of the foil to elevatedtemperatures, when attached to a metal sheet of a different metal. Asdiscussed above, tarnish is a particular problem when the metal foil isattached or held adjacent to a metal sheet. Usually the tarnish isobserved on the side of the metal foil facing the metal sheet, since theother side of the foil may already be bonded to and/or coated with thelaminating materials which coat or bond to this surface and thus protectit from the environment. However, the tarnish may also be observed onthe side of the metal foil facing away from the metal sheet. In theabsence of the inventive treatment, the tarnish occurs particularly inmetal foils, such as copper, attached to metal sheets made of relativelymore active metals, such as aluminum. Treating metal foil by contactingthe surface of a metal foil with an inert silane, titanate or zirconatecompound in accordance with the present invention forms a protectivefilm or layer on the metal foil surface which resists tarnish resultingfrom the foil being attached to a metal sheet of a metal other than themetal of the metal foil.

Attachment of Metal Foil to Metal Sheet

Referring now to the drawing figures, as shown therein, in eachembodiment of the present invention, the metal foil is first treatedwith, and includes a protective film or layer of, the inert silane,titanate or zirconate of the present invention so as to provide themetal foil with improved resistance to tarnish, such as that which hasbeen observed to result from the attachment to the metal sheet in theabsence of such treatment. In the drawing figures, like parts are givenlike reference numbers in each figure.

First Embodiment

FIG. 1 is a schematic cross-sectional view of an embodiment in which asingle metal foil, treated with a tarnish resistance-imparting inertsilane to form a protective layer or film, is attached to a metal sheet,in accordance with the present invention. In the embodiment illustratedin FIG. 1, the article is designated “FS,” since a single metal foil isattached to a metal sheet. In an embodiment in which the metal foil iscopper foil, the metal sheet is aluminum and the single copper foil isattached to one side of the aluminum sheet, the article is referred toas “CA.”

As shown in FIG. 1, in this embodiment, an article 10 comprises a singlesheet of a metal foil 12 which is adhered to a first side 14 of a metalsheet 16, to form the “FS” article 10. A first surface 18 of the metalfoil 12 has been treated with, and the FS article 10 includes aprotective layer 20 of, an inert silane. As shown in FIG. 1, the metalfoil 12 may include an optional treatment layer 22 on the second surface24 thereof, i.e., the second surface 24 is opposite to the first surface18 which has been treated with the inert silane to form the protectivelayer 20 and attached to the metal sheet 16. The metal foil 12 with theprotective layer 20 may be attached to the metal sheet 16 by an adhesive(not shown in FIG. 1). As noted above, when the metal foil 12 is copper,and the metal sheet 16 is aluminum, the article 10 may be referred to asa CA article. The metal sheet 16 may be treated with a release material(not shown) prior to attachment to the metal foil.

Second Embodiment

FIG. 2 is a schematic cross-sectional view of an embodiment in which twometal foils, each treated with a tarnish resistance-imparting inertsilane to form respective protective layers or films, are attached toopposite sides of a metal sheet, in accordance with the presentinvention, to form an article referred to generally as “FSF.” In anembodiment in which the metal foil is copper foil, the metal sheet isaluminum and two copper foil are attached to opposite sides of thealuminum sheet, the article is referred to as “CAC.”

As shown in FIG. 2, a composite article 30 comprises two sheets of ametal foil 12 a and 12 b, each of which are adhered to opposite surfaces14 and 32 of a single metal sheet 16, to form the “FSF” article 30. Afirst surface 18 a and 18 b of each respective metal foil 12 a and 12 bhas been treated with, and the FSF article 30 thus includes twoprotective layers 20 a and 20 b of an inert silane. As shown in FIG. 2,each metal foil 12 a and 12 b may include an optional treatment layer 22on respective second surfaces 24 a and 24 b, i.e., the surfaces of eachmetal foil opposite to the first surface which has been treated with aninert silane and which will be attached to the metal sheet 16. The metalfoils 12 a and 12 b, each with the respective protective layer 20 a and20 b, may be attached to the metal sheet 16 by an adhesive (not shown inFIG. 2). As noted above, when each metal foil 12 a and 12 b is copper,and the metal sheet 16 is aluminum, the article 30 may be referred to asa CAC article. The metal sheet 16 may be treated with a release material(not shown) prior to attachment to the metal foil.

FIG. 3 is a schematic plan view of a composite article which may be anFS article or an FSF article. In FIG. 3, the article is designated asthe FS article 10 described above and shown in FIG. 1, (it is understoodthat a similar view would appear of, and a similar description wouldapply to, the FSF article of FIG. 2). In the article 10 shown in FIG. 3,the metal foil 12 is shown partially peeled back. The metal foil 12 hasbeen treated with, and includes a protective layer 20 of a tarnishresistance-imparting inert silane. The metal foil 12 has been attachedto a metal sheet 16, in accordance with the present invention. As shownin FIG. 3, the FS article 10 is viewed with the second surface 24 of themetal foil 12 (which has not been treated with the inert silane of thepresent invention) facing upwardly and peeled back at one corner 36. Thepeeled-back corner 36 of the metal foil 12 exposes the protective layer20 on the metal foil 12 which has been formed by treatment of the metalfoil 12 with an inert silane, titanate or zirconate in accordance withthe present invention. The metal foil 12 as shown in FIG. 3 does notinclude a treatment layer 22, but such may of course be included.

As described in more detail above, the FS component shown in FIG. 3 mayinclude a metal sheet of aluminum which may be, for example, from about1 mil (0.025 mm) to about 25 mils (0.63 mm)in thickness. Similarly, themetal foil attached to the metal sheet may be, for example, ½ oz. copperfoil, i.e., about 0.7 mil (0.018 mm) in thickness.

As shown in FIG. 3, a band of flexible adhesive 40 extends around theperiphery of the FS article 10 near or at the outer edge of the article(the flexible adhesive 40 is shown in phantom in the portions of thearticle in which the metal foil is not folded back). The band offlexible adhesive 40 is located in an adhesive application zone definedby the dotted line 42 and the edge of the FS article 10. In thisembodiment, the flexible adhesive attaches the metal foil 12 to themetal sheet 16. The adhesive 40 may be applied to the protective layer20 or to the surface of the metal sheet 16 at the respective borders ofthe metal foil 12 and the metal sheet 16. The central zones of the metalfoil 12 and the metal sheet 16, inside a border line 44, are notattached to each other, but are normally in contact with each other.Generally, it is this adjacent but non-attached central zone inside theborder 44 of the metal foil 12 which may become tarnished in the absenceof treatment with the inert silane in accordance with the presentinvention.

The flexible adhesive band 40 may be applied in the adhesive applicationzone 42 in a width from about 0.01 to about 0.5 inches (about 0.25 mm toabout 12.5 mm) depending upon both the end product requirements and thesize of the sheets of aluminum and copper being used. In one embodiment,the flexible adhesive band 40 is from about 0.030 inch (0.75 mm) toabout 0.090 inch (2.3 mm) in width. In one embodiment, the flexibleadhesive band 40 is from about 0.001 inch (0.025 mm) to about 0.005 inch(0.125 mm) in thickness. In one embodiment, the flexible adhesive band40 is from about 0.001 inch (0.025 mm) to about 0.002 inch (0.05 mm) inthickness. The amount and thickness of the adhesive should be sufficientto maintain the metal foil in position on the metal sheet during thesteps in which the article is processed.

The adhesive may be any flexible adhesive. The exact nature of theadhesive is not critical, however, it should be capable of adhering tothe inert silane and to any release material applied to the metal sheet.The portion of the foil comprising the application zone 42 may be cutaway from the remaining portions subsequently in the processing to form,e.g., PCBs.

As shown in FIG. 3, the central non-joined zone defined by the border 44spaced inwardly from the adhesive application zone 42 is designed toform the finished circuit board. In addition to the adhesive 40, in oneembodiment additional spots 50 of adhesive are included in a band 46which lies outwardly from the central zone border line 44 and inwardlyof the adhesive application zone line 42. Portions of the band 46 may beused, e.g., for making test portions of small boards for quality controlpurposes. The additional spots 50 of adhesive may comprise the same or adifferent adhesive as that used for the flexible adhesive 40.

In the embodiments shown in FIGS. 1-3, surface(s) of the metal sheet towhich the metal foil(s) will be attached may be clean, i.e., virginmetal untreated in any way other than cleaning, such as degreasingand/or washing. The metal sheet 16 may be treated with a releasematerial. The release material may be a polymeric resin initiallyapplied, for example, by a spraying process which deposits a coating ofrelease material from about 1 to about 5 microns in thickness on themetal sheet 16. If the release material is applied from a solution, inthe drying and curing process, solvent in the release material flashesoff, leaving the coating. The polymeric resin may be one of a number ofresins which are thermally stable to approximately 375° C. Exemplarypolymeric resins are disclosed in U.S. Pat. No. 4,875,283, which isincorporated herein by reference for its teachings of such releasematerials. In one embodiment, the release material is asilicon-containing polymerizable resin sold under the trade nameFREKOTE® 700 or FREKOTE® 700-NC by FREKOTE, Inc., a subsidiary of theDexter Corporation of Seabrook, N.H. The release material applied to themetal sheet provides for easier separation of the metal foil from themetal separator sheet after lamination.

A standard size sheet of copper foil employed in making PC boards todayis 12×12 inches. Another standard size is 18×24 inches. Sheets as largeas 48×72 are sometimes used. Sheets 36×48 inches may be cut into fourseparate sheets of 18×24 inches. Other in-between sizes may be used aswell.

Third Embodiment

In a third embodiment, the invention relates to an article for use inprinted circuit board manufacture, including a metal sheet of a firstmetal, the metal sheet having a length and width; a pair of metal foils,both formed of a second metal which is different from the first metal.In this embodiment, a first side of each metal foil is adjacent a sideof the metal sheet, and this first side of the metal foil has bondedthereto a protective film. The protective film may have a thickness fromabout 0.001 microns to about 1 micron. The protective film is formed ofan inert silane, titanate or zirconate compound. In this embodiment,each of the pair of metal foils has a length and width greater than thelength and width of the metal sheet, and the pair of metal foils areadhered to each other in the areas of each metal foil which extendbeyond the periphery of the metal sheet. Except as noted, the metal foiland the metal sheet of this embodiment may be essentially the same asdescribed above with respect to the first (FS) and second (FSF)embodiments.

The composite article of the third embodiment may be made by a method inwhich metal foils of any particular type and thickness described hereinare joined to a metal sheet of any particular type of alloy andthickness described herein, such that the edges of the metal foilsextend beyond the edges of the metal sheet, the metal foil edges areattached to each other, and the metal foil is adjacent to but is notdirectly attached to the metal sheet by any means. Such an assemblysimplifies later assembly of multilayer press packets or books.

In this embodiment, the pair of metal foils are placed on both sides ofthe metal sheet. The metal foils are attached to each other in a regionoutside the useful surface of the metal foil. This arrangement allowsfor thermal expansion of the metal sheet with no danger of wrinkling,stretching or otherwise deforming the metal foil. This arrangement maybe referred to as a foil-to-foil article, or, using the abovenomenclature, a F-to-F article. Thus, for example, in the case of copperfoils, the article would be a copper-to-copper article, i.e., a C-to-Carticle. While not specifically identified in this designation, theF-to-F and C-to-C composite articles each include a metal sheetsandwiched between the pair of metal foils.

The metal foils may be attached to each other by a suitable adhesive, bywelding, by soldering, or by any other means for attaching a pair ofmetal foils to each other. Since the attached portions of the metal foilin a foil-to-foil article are intended to be discarded, the attachmentmaterial or means for attaching the foils is not critical to theinvention.

FIG. 4 is a schematic cross-sectional view of an embodiment in which twometal foils, each treated with a tarnish resistance-imparting inertsilane to form a protective layer or film, are attached to oppositesides of a metal sheet, in accordance with the present invention, toform an article referred to generally as “F-to-F.” In an embodiment inwhich the metal foil is copper foil, the metal sheet is aluminum and twocopper foils are attached to each other opposite sides of the aluminumsheet, the article is referred to as “C-to-C.” The reference numbersused in FIG. 4 are the same as in FIGS. 1 and 2 where the identifiedelements are the same.

As shown in FIG. 4, a composite article 60 comprises two sheets of ametal foil 12 a and 12 b, each of which are held adjacent to oppositesurfaces 14 and 32 of a single metal sheet 16, to form the “F-to-F”article 60. A first surface 18 a and 18 b of each respective metal foil12 a and 12 b has been treated with, and the F-to-F article 60 thusincludes two protective layers 20 a and 20 b of an inert silane,titanate or zirconate in accordance the present invention. As shown inFIG. 4, each metal foil 12 a and 12 b may include an optional treatmentlayer 22 on respective second surfaces 24 a and 24 b, i.e., the surfacesof each metal foil opposite to the first surface which has been treatedwith an inert silane and which will be attached to the metal sheet 16.The metal foils 12 a and 12 b, each with the respective protective layer20 a and 20 b, are adjacent, but not attached to, the metal sheet 16.The metal foils 12 a and 12 b are attached to each other by anattachment material 52 at a portion of each foil which extends beyond aperiphery 54 of the metal sheet 16. The attachment material 52 may be anadhesive, a weld, a soldering or other known attachment materials ormeans for attaching together metal foils, e.g., a chemical bond. Theadhesive, for example, may be a thermoplastic adhesive or athermosetting adhesive. The adhesive may be an epoxy or a polyacrylateor polymethacrylate. The weld may be by any standard weld useful formetal foils. The soldering may be by any standard solder useful formetal foils. In one embodiment, the solder is free of added lead. Theexact nature of the attachment material is not critical.

The portions of the metal foils 12 a and 12 b extending beyond theperiphery 54 of the metal sheet 16 may be removed and the metal foilrecycled subsequent to lamination of the article.

FIG. 5 is a schematic plan view of the F-to-F composite article 60, inaccordance with this embodiment of the present invention. In FIG. 5, thearticle 60 is shown with the metal foil 12 a partially peeled-back. Thearticle 60 further includes a second metal foil 12 b. Both of the metalfoils 12 a and 12 b have been treated with, and each includes aprotective layer 20 of a tarnish resistance-imparting, inert silane,titanate or zirconate. The metal foils 12 a and 12 b have been placedadjacent to a metal sheet 16, in accordance with the present embodiment.As shown in FIG. 5, the F-to-F article 60 is viewed with the secondsurface 24 a of the metal foil 12 a (which second surface 24 a has notbeen treated with the inert silane of the present invention) facingupwardly and peeled back at one corner 36. The peeled-back corner 36 ofthe metal foil 12 a exposes the protective layer 20 on the metal foil 12a which has been formed by treatment of the metal foil 12 a with aninert silane, titanate or zirconate in accordance with the presentinvention, and allows an edge portion of the metal foil 12 b to be seenin the view shown in FIG. 5. The copper foil 12 a as shown in FIG. 5does not include a treatment layer 22, but such may of course beincluded, as shown in FIG. 4.

As described in more detail above, the F-to-F component shown in FIG. 5may include a metal sheet of commercial grade aluminum which may be, forexample, from about 1 mil (0.025 mm) to about 25 mils (0.63 mm)inthickness. Similarly, the metal foil attached to the metal sheet may be,for example, ½ oz. copper foil, i.e., about 0.7 mil (0.018 mm) inthickness.

As shown in FIG. 5, a band of the attachment material 52 extends aroundthe periphery 54 of the F-to-F article 60 near the edge of the copperarticle where the metal foils extend beyond the periphery 54 of themetal sheet 16 (the attachment material 52 is shown in phantom in theportions of the article in which the metal foil is not folded back). Theattachment material 52 attaches the first metal foil 12 a to the secondmetal foil 12 b, but not to the metal sheet 16. The attachment material52 is applied to the protective layer 20 of either or both of the metalfoils 12 a and 12 b, in the portion of the metal foil 12 a and/or themetal foil 12 b. The central zones of the metal foils 12 a and 12 b arenot attached to the metal sheet 16, but are adjacent to and are normallyin contact with the metal sheet. Generally, it is this adjacent butnon-attached area of the metal foils 12 a and 12 b which may becometarnished in the absence of treatment with the inert silane inaccordance with the present invention.

As shown in FIG. 5, the band of attachment material 52 may have a widthfrom about 10 mils to about 500 mils (about 0.25 mm to about 12.5 mm)depending upon both the end product requirements and the size of thesheets of aluminum and copper being used. In one embodiment, an adhesiveband or strip having a width from about 30 mils (0.75 mm) to about 90mils (2.3 mm) is used. In one embodiment, the band of attachmentmaterial 52 may have a thickness from about 1 mil (0.025 mm) to about 5mils (0.125 mm). In one embodiment, the band of attachment material 52has a thickness from about 1 mil (0.025 mm) to about 2 mils (0.05 mm).

As shown in FIG. 5, the central non-attached zone is defined by an outerperiphery 54 of the metal sheet 16 (the outer periphery 54 is shown inphantom in the portions of the article in which the metal foil is notfolded back). This central, non-attached zone will be incorporated inthe finished circuit board. The attached portion of the metal foils 12 aand 12 b, and the portion of these foils which extend beyond theperiphery 54 of the metal sheet 16 will be cut off and discarded.

When a plurality of the F-to-F articles comprising the pair of metalfoils and the metal sheet are clamped together and placed in themultiarticle press together with epoxy resin fabric for multilayerpressing to form “books” for use as multilayer PCBs, the metal of themetal sheet can expand in an unrestricted manner during heating withoutcausing the occurrence of surface tensions on and resultant deformationsin the metal foil. Thus, when the epoxy resin softens and flows, it canflow along the metal foil and bond thereto without coming into contactwith the metal sheet and without possibly contacting the edges of themultilayer with epoxy. The attached portions of the metal foils, whichextend beyond the periphery of the metal sheet, can then be easilyseparated along the metal sheet.

In the F-to-F embodiment, the metal foil may be somewhat larger than astandard metal foil (as described above), in order to provide theportion which extends beyond the outer periphery of the metal sheet.Thus, for example, rather than a sheet of metal foil having a dimensionof 12 inches×12 inches, the sheet may have a dimension of 13 inches×13inches.

In the absence of the protective layer formed by the tarnishresistance-imparting inert silane treatment of the present invention,during the time the metal foil, of a first metal, is attached to themetal sheet, of a second metal, the metal foil may become tarnished. Thetarnish may form during, and may not become apparent until after,lamination to a prepreg, during which time intense heat and pressure areapplied to the nascent laminate, generally in the presence of moistureand/or reactive chemical species which may be present as by-products ofchemical reactions during the lamination or as impurities in thelaminate reactants.

In one embodiment, the inventive method involves contacting the surfaceof a treated or untreated metal foil, opposite the surface of which isor will be laminated to a resin material such as an epoxy prepreg, withan inert silane, titanate or zirconate compound, and subsequentlyattaching the treated surface to a metal sheet of a metal other than themetal of the metal foil. In one embodiment, the surface of a metal foilis treated in accordance with the present invention prior to laminationof the opposite side to a resin material. In another embodiment, thesurface of a metal foil is treated in accordance with the presentinvention after lamination of the opposite side to a resin material. Inone embodiment, both sides of the metal foil are treated prior tolamination or attachment of the metal foil to the metal sheet. Thepresent invention is especially beneficial when the metal foil istreated on both sides prior to attachment to the metal sheet and priorto lamination to a resin or prepreg material.

Metal Foils

The metal foil 12 treated in accordance with the present invention maybe any metal foil that can be laminated with a resin based material,such as an epoxy prepreg. Such metal foils, when laminated to a prepregmay be used in the manufacture of printed circuit boards (PCBs). In oneembodiment, the metal foil treated in accordance with the presentinvention is an electrically conductive metal foil. In one embodiment,the metal foil may comprise copper, aluminum, nickel, tin, silver, gold,chromium, zinc, platinum, palladium, iron, lead, steel, brass, bronze,or an alloy of two or more of the foregoing metals. In one embodiment,the metal foil is copper. In one embodiment, the metal foil is acopper-based alloy. Examples of such alloys include copper-zinc,copper-silver, copper-tin, chromium-molybdenum and nickel-chromium.

The metal foil 12 may be made using any suitable method. Typically, themetal foil is made using one of two techniques. In one embodiment, thefoil is a wrought or rolled metal foil, such as copper foil, which isproduced by mechanically reducing the thickness of a metal or metalalloy strip or ingot by a process such as rolling. In one embodiment,the foil is an electrodeposited foil, which is produced byelectrolytically depositing metal ions, such as copper ions, on arotating cathode drum and then peeling the deposited metal strip fromthe cathode. In one embodiment, the metal foil is an electrodepositedcopper foil.

The metal foil 12 typically has a nominal thickness ranging from about0.2 mils (about 0.005 mm) to about 200 mils (about 2.5 mm). In oneembodiment, the metal foil has a nominal thickness in the range fromabout 2 mils (0.5 mm) to about 30 mils (0.76 mm). In one embodiment, themetal foil has a nominal thickness in the range from about 2 mils (0.5mm) to about 15 mils (0.38 mm). In one embodiment, the metal foil has anominal thickness in the range from about 6 mils (0.15 mm) to about 15mils (0.38 mm). Metal foil thickness is sometimes expressed in termsweight and typically the foils of the present invention have weights orthicknesses ranging from, for example, about ⅛ to about 14 oz/ft² (about38 g/m² to about 4280 g/m²). In one embodiment, the metal foil is acopper foil having a weight of ½, 1, 2 or 3 oz/ft² (about 153, 306, 611or 917 g/m², respectively). In one embodiment, the metal foil is acopper foil having a weight of 1 oz/ft² (306 g/m²). In one embodiment,the metal foil is a copper foil having a weight of 2 oz/ft² (611 g/m²).

Electrodeposited metal foils have a smooth or shiny (drum) side and arough or matte (metal deposit growth front) side. The side or sides ofthe metal foil which may be contacted with an inert silane, titanate orzirconate in accordance with the invention can be the rough or matteside, shiny side, or both sides. In accordance with one embodiment ofthe invention, a metal foil may have its shiny side treated. In oneembodiment, a metal foil has its matte side treated. In one embodiment,a metal foil has both matte and shiny sides treated.

The sides of the metal foil 12 may be a “standard-profile surface,”“low-profile surface” or “very-low-profile surface.” These terms may beapplied to both the matte surface and the shiny surface of the metalfoils. The term “standard-profile surface” is used herein to refer to afoil surface having an R_(tm) of about 7 microns to about 18 microns.The term “low-profile surface” refers to a foil surface having an R_(tm)of about 4 to about 7 microns. The term “very-low-profile surface”refers to a foil surface having an R_(tm) of about 1 to about 4 microns.R_(tm) is the mean of the maximum peak-to-valley vertical measurementfrom each of five consecutive sampling measurements, and can be measuredusing a Surtronic 3 profilometer marketed by Rank Taylor Hobson, Ltd.,Leicester, England.

In one embodiment, the metal foil 12 of the present invention may becharacterized by the absence of any added surface roughening treatmenton the base surface of the side or sides opposite to which the inventivemethod is practiced. The term “base surface” of a side of foil refers toa raw foil surface which has not been subjected to any subsequenttreatments of the type discussed below for refining or enhancing foilproperties and/or increasing surface roughness. The term “added surfaceroughening” refers to any treatment performed on the base surface of thefoil for the purpose of increasing the roughness of the surface of thefoil not in accordance with the inventive method. In one embodiment,added surface roughening increases the R_(tm) by 3 microns or more; andin another embodiment, added surface roughening increases the R_(tm) by10 microns or more.

In one embodiment, mechanical roughness imparted to wrought metal foilduring rolling or by subsequent abrasion which increases roughnessbeyond that of a standard profile surface is considered to be an addedsurface roughening treatment. In one embodiment, roughness imparted toan electrodeposited metal foil during electrodeposition which increasesroughness beyond that of a standard profile surface is considered to bean added surface roughening. In one embodiment, any roughness impartedto the base surface of a metal foil that increases the roughness of thefoil beyond that of a standard profile surface is considered to be addedsurface roughening. In one embodiment, any roughness imparted to thebase surface of a metal foil that increases the roughness of the foilbeyond that of a low-profile surface is considered to be added surfaceroughening. In one embodiment, any roughness imparted to the basesurface of a metal foil that increases the roughness of the foil beyondthat of a very low-profile surface is considered to be added surfaceroughening. The surface roughening may comprise, e.g., forming dendriteson the shiny side of electrodeposited foil.

In one embodiment, the base surface of the side or sides of the metalfoil is untreated prior to being subjected to the inventive method. Theterm “untreated” is used herein to refer to the base surface of a metalfoil that has not undergone subsequent treatment for the purpose ofrefining or enhancing the foil properties and/or increasing surfaceroughness. In one embodiment, the untreated foils have a naturallyoccurring, non-dendritic or non-nodular layer of a metal oxide adheredto the base surface thereof. This naturally occurring oxide layer is notan added treatment provided for refining or enhancing foil propertiesand/or increasing surface roughness.

Surface Treatments of the Metal Foil

In one embodiment, the base surface of the side or sides of the foil 12is treated, prior to being subjected to the inventive method, with oneor more surface treatment layers for the purpose of refining orenhancing the foil properties, but not to add surface roughness. Anyside of the foil which is not subjected to the inventive method can,optionally, also have one or more of such treatment layers applied toit. These surface treatments are known in the art.

For example, the surface treatments include the application of a metallayer 22 which does not increase the surface roughness wherein the metalis indium, tin, nickel, cobalt, copper alloy such as copper-tin alloy,and mixtures of two or more thereof, prior to practicing the inventivemethod. Metal layers of this type are sometimes referred to as barrierlayers. These metal layers preferably have thicknesses in the range ofabout 0.01 to about 1 micron, more preferably about 0.05 to about 0.1micron.

The surface treatments also include the application of a metal layer 22which does not increase the surface roughness, wherein the applied metallayer comprises tin, nickel, molybdenum, chromium, chromium-zinc, zinc,aluminum, or a mixture of two or more thereof, prior to practicing theinventive method. Metal layers of this type are sometimes referred to asstabilization layers. These stabilization layers can be applied to thebase surface of the foil, or they can be applied to a previously appliedbarrier layer. In one embodiment, the stabilization layer has athickness in the range of about 0.005 to about 0.05 micron. In oneembodiment, the stabilization layer has a thickness in the range fromabout 0.01 to about 0.02 micron. The metals applied as a surfacetreatment may include metals in a metallic, metal oxide or metal nitrideform. The metals may be applied by known methods, e.g., byelectrodeposition or by a vapor deposition method. Examples of suchmetals and methods for application thereof are disclosed, e.g., in U.S.Pat. No. 5,908,544.

In one embodiment, one or both sides of the metal foil 12 is firsttreated with at least one barrier layer to form the layer 22. In anotherembodiment, one or both sides of the foil is first treated with at leastone stabilization layer. In yet another embodiment, one or both sides ofthe foil is first treated with at least one barrier layer, then at leastone of the treated sides is treated with at least one stabilizationlayer prior to practicing the inventive method.

The metal foil 12 in accordance with this invention can be a singlelayer metal foil, such as a copper foil, an aluminum foil or a nickelfoil, or a foil of a metal alloy. The metal foil in accordance with thisinvention can be a foil containing multiple layers of a metal or metalalloy, such as a foil made of layers of copper and brass. There is noparticular limit to the number of metal layers in any given metal foil.

In one embodiment, the inventive process optionally involves initiallycontacting the metal foil 12 with an acidic solution. An acidic solutionhas a pH of less than about 5, and preferably less than about 3, andmore preferably less than about 2. The acidic solution contains an acidand a solvent such as water, polar organic liquids such as alcohols andglycols, and mixtures thereof. Contacting the metal foil with the acidicsolution serves to remove surface oxides from the metal foil andotherwise clean the surface of the metal foil. Additionally, in someinstances, contact with the acidic solution before application of theinert silane, titanate or zirconate compound facilitates the inventivetreatment.

The metal foil is contacted with the acidic solution in any suitablemanner including but not limited to dipping, spraying, wiping, immersingand the like. In one embodiment, the metal foil is immersed in theacidic solution. In another embodiment, the temperature of the acidicsolution is from about 20° C. to about 60° C. In one embodiment, thetemperature of the acidic solution is from about 30° C. to about 40° C.

The acidic solution contains an acid and a suitable solvent. In oneembodiment, the solvent is water. In one embodiment, polar organicliquids are used as the solvent. In one embodiment, combinations ofwater and polar organics are used as the solvent. In one embodiment,inorganic acids are used. In one embodiment, organic acids are used.

Examples of inorganic acids which may be utilized in the acidic solutioninclude halogen acids such as hydrofluoric acid, hydrochloric acid,hydrobromic acid and hydriodic acid, sulfuric acid, sulfurous acid,nitric acid, perchloric acid, boric acid and phosphorus acids such asphosphorous acid and phosphoric acid, and combinations thereof. Nitricacid and sulfuric acid are preferred inorganic acids.

Examples of organic acids include carboxylic and polycarboxylic acidssuch as formic acid, acetic acid, propionic acid, citric acid, oxalicacid, etc.; organic phosphorus acids such as dimethylphosphoric acid anddimethylphosphinic acid; or sulfonic acids such as methanesulfonic acid,ethanesulfonic acid, 1-pentanesulfonic acid, 1-hexanesulfonic acid,1-heptanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, etc,and combinations thereof.

In one embodiment, after the metal foil has contacted the acidicsolution, the metal foil is rinsed with a neutral solution. In oneembodiment, water is used. In one embodiment, deionized water is used.In one embodiment, distilled water is used. In one embodiment waterwhich has been treated with activated carbon to remove organics is used.Of course, such water treatments may be combined. The neutralizing orrinsing solution serves to remove excess acid from the surface of themetal foil in addition to neutralizing the surface of the metal foil.

Protective Film Formed by an Inert Silane, Titanate or Zirconate

In one embodiment, an article according to the present inventionincludes on the metal foil 12 a protective film or layer 20 of an inertsilane, titanate or zirconate, which is applied by contacting the metalfoil 12 with an inert silane, titanate orzirconate compound, typicallyvia a solution of the inert silane, titanate orzirconate. In oneembodiment, an inert silane, titanate orzirconate compound is applieddirectly to the surface 18 of the metal foil 12, to form the protectivelayer 20.

The inert silane compounds used to form the protective layer 20 includehydrocarbylsilanes, fluorocarbonsilanes and other inert silane compoundsthat bond to the metal foil and which thereafter present an inert outeror outwardly-facing surface which protects the surface of the metal foilfrom tarnish. In one embodiment, the inert silane, titanate andzirconate compounds have hydrocarbyl or substantially hydrocarbyl groupshaving from about 5 to about 20 carbon atoms attached to a centralsilicon, titanium or zirconium atom. In these inert silane, titanate andzirconate compounds, the compound bonds to the metal foil by one or morereactive groups and thereafter presents an inert outer oroutwardly-facing surface which protects the surface of the metal foilfrom tarnish. In one embodiment, the hydrocarbyl groups in the inertsilane, titanate and zirconate compound contains about 5 to about 100carbon atoms. In one embodiment, the hydrocarbyl group in the inertsilane, titanate and zirconate includes about 20 to about 60 carbonatoms. In one embodiment, the hydrocarbyl group in the inert silane,titanate and zirconate includes about 1 to about 20 carbon atoms. In oneembodiment, the hydrocarbyl group in the inert silane, titanate andzirconate includes about 1 to about 8 carbon atoms. In one embodiment,the hydrocarbyl group in the inert silane, titanate and zirconateincludes about 1 to about 4 carbon atoms.

The term “hydrocarbyl” includes hydrocarbon as well as substantiallyhydrocarbon groups. “Substantially hydrocarbon” describes groups whichcontain heteroatom substituents which do not alter the predominantlyhydrocarbon nature of the group; that is, a substantially hydrocarbonsubstituent provides the same or substantially the same “inertness” tothe inert silane, titanate or zirconate as would a purely hydrocarbonsubstituent of similar structure absent the substitution. Examples ofhydrocarbyl groups include the following: (1) hydrocarbon substituents,i.e., aliphatic (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl,cycloalkenyl) substituents, aromatic-, aliphatic- andalicyclic-substituted aromatic substituents and the like as well ascyclic substituents wherein the ring is completed through anotherportion of the molecule (that is, for example, any two indicatedsubstituents may together form an alicyclic radical), examples of suchgroups are methyl, ethyl, cyclohexyl, phenyl and tolyl; (2) substitutedhydrocarbon groups, that is, groups containing non-hydrocarbonsubstituents which, in the context of this invention, do not alter thepredominantly hydrocarbon, i.e., inert, nature of the substituent; thoseskilled in the art will be aware of such groups (e.g., fluoro, chloro,etc.); and (3) heteroatom-containing substituents, i.e., substituentswhich, while having a predominantly hydrocarbon character within thecontext of this invention, contain an atom other than carbon present ina ring or chain otherwise composed of carbon atoms (e.g., alkoxy, ether,mercaptan).

In general, no more than about 2 hetero substituents (on average) arepresent for every ten carbon atoms in the hydrocarbyl group. In oneembodiment, no more than about 1 hetero substituent (on average) ispresent for every ten carbon atoms in the hydrocarbyl group. In oneembodiment, there are no such hetero atom substituents in thehydrocarbyl group. In one embodiment, the hydrocarbyl group is one of anunsubstituted alkyl group, an unsubstituted cyclic alkyl group, or anunsubstituted aromatic group.

General examples of inert silane compounds include alkyl silanes,cycloalkyl silanes, aromatic silanes, substituted aromatic silanes, andfluorocarbon silanes. In one embodiment, the inert silane compound maybe represented by the formula

wherein G¹, G², G³, G⁴, G⁵ and G⁶ are independently hydrocarbyl, orhydrocarbyloxy groups; R¹ is a hydrocarbyl group; and n is zero or 1. Inone embodiment at least one of each of G¹, G², G³, G⁴, G⁵ and G⁶ may beindependently alkoxy, and R¹ may be an alkylene group of up to about 10carbon atoms, or an aryl group of up to about 10 carbon atoms. In oneembodiment, at least one of G¹, G², G³, G⁴, G⁵ and G⁶ is a hydrocarbylgroup or a fluorocarbon group. In one embodiment, at least one of G¹,G², G³, G⁴, G⁵ and G⁶ is an alkoxy group and the remainder areindependently hydrocarbyl groups or fluorocarbon groups. In oneembodiment each of G¹, G², G³ and G⁶ is an alkoxy group of up to about10 carbon atoms, G⁴ and G⁵ are hydrocarbyl and n is one. In oneembodiment, at least two of G¹, G², G³, G⁴, G⁵ and G⁶ are alkoxy and theremainder are independently hydrocarbyl groups or fluorocarbon groups.Examples of such inert silane compounds include1,2-bis(trimethoxysilyl)ethane, 1,2-bis(dimethoxyethylsilyl)ethane,bis(trimethoxysilylethyl)benzene, 1,6-bis(trimethoxysilyl)hexane and1,6-bis(diethoxyethylsilyl)hexane.

In another embodiment, the inert silane compound may be a compoundrepresented by the formula

wherein R², R³, R⁴ and R⁵ are independently hydrogen, a hydrocarbylgroup, a fluorocarbon group, a hydrocarbyloxy group, or a hydroxy group.In one embodiment, each of R³, R⁴ and R⁵ are either methoxy or ethoxy,and R² is a hydrocarbyl group or a fluorocarbon group. In oneembodiment, each of R⁴ and R⁵ are methoxy or ethoxy, and R² and R³ arehydrocarbyl groups.

Examples of these inert silane compounds include methyltrimethoxysilane;ethyltrimethoxysilane; propyltrimethoxysilane; n-butyltrimethoxysilane;isobutyltrimethoxysilane; pentyltrimethoxysilane; hexyltrimethoxysilane;octyltrimethoxysilane; 7-oct-1-enyltrimethoxysilane;phenyltrimethoxysilane; the corresponding ethoxy and propoxysubstituents replacing the methoxy substituents; hydrocarbyl substitutedphenyltrimethoxysilanes such as p-(methyl)phenyltrimethoxysilane;3-cyclopentadienylpropyl trimethoxysilane; vinyl trimethoxysilane; allyltrimethoxysilane; methoxypropyl trimethoxysilane; methyltriethoxysilane; ethyl triethoxysilane; propyl triethoxysilane; n-butyltriethoxysilane; isobutyl triethoxysilane; pentyl triethoxysilane; hexyltriethoxysilane; octyl triethoxysilane; 7-oct-1-enyl triethoxysilane;phenyl triethoxysilane; hydrocarbyl substituted phenyl triethoxysilanesuch as p-(methyl)phenyl triethoxysilane; 3-cyclopentadienylpropyltriethoxysilane; vinyl triethoxysilane; allyl triethoxysilane;methoxypropyl triethoxysilane; methyl triisopropoxysilane; ethyltriisopropoxysilane; propyl triisopropoxysilane; vinyltriisopropoxysilane; vinyl tris-t-butoxysilane; 3,3,3-trifluoropropyltrimethoxysilane; and tridecafluoroctyl triethoxysilane.

Mixtures of two or more of the inert silane compounds listed above maybe used. For example, in one embodiment, the inert silane compound ismethyltrimethoxysilane or isobutyltrimethoxysilane in combination withpropyltrimethoxysilane. In another embodiment, the inert silane compoundis a fluorocarbonsilane in combination with an alkyl silane. In yetanother embodiment, the inert silane compound is 3,3,3-trifluoropropyltrimethoxysilane in combination with propyl trimethoxysilane.

The titanate compounds that may be used to form the protective layer 20include di(cumyl)phenyl oxoethylene titanate; di(dioctyl)pyrophosphateoxoethylene titanate; isopropyl triisostearoyl titanate; isopropyldimethacryl isostearoyl titanate; isopropyl tri(dodecyl)benzenesulfonyltitanate; isopropyl tri(dioctyl)phosphato titanate; isopropyl(4-amino)benzenesulfonyl di(dodecyl)benzenesulfonyl titanate; isopropyltri(dioctyl)pyrophosphato titanate; tetraoctyl di(ditridecyl)phosphitotitanate; tetra (2,2 diallyoxymethyl)butyl,di(ditridecyl)phosphitotitanate; neopentyl(diallyl)oxy, trineodecanonyl titanate;neopentyl(diallyl)oxy-tri(dodecyl)benzene-sulfonyl titanate;neopentyl(diallyl)oxy-tri(dioctyl)phosphato titanate;neopentyl(diallyl)oxy-tri(dioctyl)pyrophosphato titanate; and mixturesof two or more thereof. These compounds are sometimes referred to astitanate coupling agents.

The zirconate compounds that may be used to form the protective layer 20include neopentyl(diallyl)oxy-tri(dioctyl)phosphato zirconate. Thesecompounds are sometimes referred to as zirconate coupling agents.

Mixtures of two or more of the foregoing silane, titanate and/orzirconate compounds can be used to form the protective layer 20.

The inert silane, titanate or zirconate compound solution may be in theform of a dispersion or solution in water, a mixture of water andalcohol, or a suitable organic solvent, or as an aqueous emulsion of theinert silane, titanate or zirconate compound, or as an aqueous emulsionof absolution of the inert silane, titanate or zirconate compound in asuitable organic solvent. Conventional organic solvents may be used.These include alcohols, ethers, ketones, and mixtures of these withaliphatic or aromatic hydrocarbons or with amides such asN,N-dimethylformamide. Useful solvents are those having good wetting anddrying properties and include, for example, water, methanol, ethanol,isopropanol, and methylethylketone. Aqueous emulsions of the inertsilane, titanate or zirconate compound may be formed in conventionalmanner using conventional dispersants and surfactants, includingnonionic dispersants.

In one embodiment, the step of contacting the metal foil with the inertsilane, titanate or zirconate solution may be repeated, if desired,several times. However, a single step gives generally useful resultsand, hence, in one embodiment the contacting step is a single step, notrepeated. Contact is accomplished via suitable application methods whichinclude reverse roller coating, doctor blade coating, dipping,immersing, painting and spraying, although immersing the metal foil inthe inert silane, titanate or zirconate solution is preferred.

In one embodiment, the inert silane, titanate or zirconate compound ispresent in the solution in an amount from about 0.01% to about 10% v/v.In another embodiment, the inert silane, titanate or zirconate compoundis present in the solution in an amount from about 0.05% to about 5%v/v. In yet another embodiment, the inert silane, titanate or zirconatecompound is present in the solution in an amount from about 0.1% toabout 2% v/v.

In one embodiment, the inert silane, titanate orzirconate compound orthe inert silane, titanate or zirconate compound solution are at atemperature from about 10° C. to about 50° C. during the step ofcontacting the foil with the inert silane, titanate or zirconate. Inanother embodiment, the inert silane, titanate or zirconate compoundsolution is at a temperature from about 15° C. to about 40° C. duringthe step of contacting. In yet another embodiment, the inert silane,titanate or zirconate compound solution is at a temperature from about20° C. to about 30° C. during the step of contacting.

In one embodiment, during the step of contacting the metal foil is incontact with the inert silane, titanate or zirconate compound solutionfor a time sufficient for a protective film to form on a surface of themetal foil. In one embodiment, the metal foil is in contact with theinert silane, titanate or zirconate compound solution from about 1second to about 10 minutes. In another embodiment, the metal foil is incontact with the inert silane, titanate or zirconate compound solutionfrom about 5 seconds to about 100 seconds. In one embodiment, after themetal foil is contacted with the inert silane, titanate or zirconatecompound solution during the step of contacting, the metal foil ispermitted to dry. In one embodiment, the metal foil is heated for asuitable period of time to drive off solvent and form an inert silane,titanate or zirconate compound film. In one embodiment, the metal foilis heated to a temperature from about 50° C. to about 170° C. In anotherembodiment, the metal foil is heated to a temperature from about 70° C.to about 150° C. In one embodiment, the metal foil is heated for about 1second to about 5 minutes. In another embodiment, the metal foil isoptionally heated for about 10 seconds to about 2 minutes.

The inventive treatment forms a protective film on at least one surfaceof the metal foil. The protective film may be continuous, substantiallycontinuous or non-continuous, so long as the film prevents tarnish fromforming on the treated metal foil surface. In one embodiment, theprotective film is continuous or at least substantially continuous overthe treated metal foil surface. In one embodiment, the protective filmof the inert silane, titanate or zirconate compound on the metal foilhas a thickness from about 0.001 to about 1 micron. In anotherembodiment, the protective film of the inert silane, titanate orzirconate compound on the metal foil has a thickness from about 0.0025to about 0.1 microns. In yet another embodiment, the protective film ofthe inert silane, titanate or zirconate compound on the metal foil has athickness from about 0.005 to about 0.05 microns.

In one embodiment, the inert silane, titanate or zirconate compoundsolution contains certain additives. In one embodiment, the inertsilane, titanate or zirconate compound solution does not contain anyadditives. In another embodiment, the inert silane, titanate orzirconate compound solution contains as an additive one or more triazolecompounds. Triazole compounds include aminotriazoles, benzotriazole,hydroxybenzotriazole, alkyl substituted benzotriazoles such asmethylbenzotriazole, and carboxylbenzotriazole. In one embodiment, theinert silane, titanate or zirconate compound solution contains fromabout 0.01 g/l to about 10 g/l of one or more of the foregoing triazoleadditives. In another embodiment, the inert silane, titanate orzirconate compound solution contains from about 0.1 g/l to about 5 g/lof one or more of the foregoing triazole additives.

In one embodiment, the inert silane, titanate or zirconate compoundsolution is metal free; that is, the inert silane, titanate or zirconatecompound solution is characterized by the absence of added metals ormetal compounds (other than the titanium of the titanate and thezirconium of the zirconate). In some instances metal compoundsdeleteriously affect the resultant inert silane, titanate orzirconatecompound film formed. In one embodiment, after the metal foil is treatedin accordance with the invention, no electrolytic step is performed.

The absence of additional electrolytic steps simplifies methods ofmaking metal foil as well as simplifying the fabrication of laminatesfor printed circuit boards. In one embodiment, after the metal foil hascontacted the inert silane, titanate or zirconate compound, during thestep of contacting the metal foil is rinsed with a neutral solution. Inone embodiment, the metal foil is rinsed with water. In one embodiment,the metal foil is rinsed with deionized water. In one embodiment,distilled water is used. In one embodiment water which has been treatedwith activated carbon to remove organics is used. Of course, such watertreatments may be combined. The rinse serves to remove excess materialsfrom the surface of the treated metal foil.

Metal Sheets

The metal of which the metal sheet 16 may be formed is not limited toany particular metal. In one embodiment, the metal sheet 16 is aluminum.In one embodiment, the metal sheet 16 comprises aluminum. In oneembodiment, the metal sheet 16 is an aluminum alloy. In one embodiment,the metal sheet 16 is an aluminum alloy formulated to provide enhancedhardness with respect to aluminum. In general, aluminum is preferred foreconomic reasons, since the aluminum sheet may be used one time anddiscarded for recycling and remanufacture, rather than being reusedafter possible contamination by handling and use.

In one embodiment, the metal sheet 16 is a metal other than aluminum. Inone embodiment, the metal sheet comprises an alloy containing copper. Inone embodiment, the metal sheet comprises iron. In one embodiment, themetal sheet is stainless steel. In other embodiments, the metal sheetmay comprise aluminum, nickel, tin, silver, gold, chromium, zinc,platinum, palladium, iron, lead, steel, brass, bronze, alloys thereofand alloys of any of the foregoing metals with copper. Examples of suchalloys include copper-zinc, copper-silver, copper-tin,chromium-molybdenum and nickel-chromium. In one embodiment, the metalsheet comprises an alloy of aluminum with one or more of tin, zinc,titanium, silicon, copper, manganese, magnesium and chromium. In oneembodiment, the metal sheet comprises an alloy of aluminum, iron, tin,zinc, titanium, silicon, copper, manganese, magnesium and chromium.

In one embodiment, the metal sheet 16 is a metal which is more active onthe electrochemical scale than is the metal of which the metal foil isformed. For example, aluminum is a more active metal than copper. Inother embodiments, the metal sheet may be a metal other than aluminum.In general, the metal of the metal sheet is different from the metal ofthe metal foil. In other embodiments, the metal of the metal sheet maybe another metal selected from those mentioned above. In someembodiments, economic considerations dictate that the metal of the metalsheet be a more electrochemically active metal than the metal of themetal foil, since such metals may be more economical to use. Thedifference in electrochemical activities between the different metalsgive rise to the need for the present invention. In the absence ofapplication of the method of the present invention, tarnish of the metalfoil results from the electrochemical force generated by the differencein electrochemical activities between the different metals. Thus, thepresent invention allows use of more electrochemically active but lessexpensive metals, without sacrificing the quality of the metal foil.

The metal sheet 16 may have a thickness ranging from about 1 mil (0.025mm)to about 250 mils inch (6.35 mm). In one embodiment, the metal sheetmay have a thickness ranging from about 5 mils (0.125 mm) to about 25mils (0.63 mm). In one embodiment, the metal sheet may have a thicknessranging from about 10 mils (0.25 mm) to about 20 mils (0.5 mm). In oneembodiment, the metal sheet may have a thickness ranging from about 5mils (0.125 mm) to about 15 mils (0.375 mm). In one embodiment, themetal sheet may have a thickness ranging from about 15 mils (0.375 mm)to about 25 mils (0.63 mm).

In the embodiment shown in FIGS. 4-5, surfaces of the metal sheet towhich the metal foils will be adjacent may be clean, i.e., virgin metaluntreated in any way other than cleaning, such as degreasing and/orwashing. The metal sheet 16 may be treated with a release material. Therelease material is a polymeric resin initially applied, for example, bya spraying process which deposits a coating of release material fromabout 1 to about 5 microns in thickness on the metal sheet 16. If therelease material is applied from a solution, in the drying and curingprocess, solvent in the release material flashes off, leaving thecoating. The polymeric resin may be one of a number of resins which arethermally stable to approximately 375° C. Exemplary polymeric resins aredisclosed in U.S. Pat. No. 4,875,283, which is incorporated herein byreference for its teachings of such release materials. In oneembodiment, the release material may be a silicon-containingpolymerizable resin sold under the trade name FREKOTE® 700 or FREKOTE®700-NC by FREKOTE, Inc., a subsidiary of the Dexter Corporation ofSeabrook, N.H. As noted above, the release material provides for easierseparation of the metal foils from the metal separator sheet.

Laminates

As noted, the metal foils treated in accordance with the presentinvention can be bonded to dielectric substrates on the side opposite tothe side attached or adjacent to the metal sheet. With the inventivefoils, either the matte side or shiny side can be bonded to a dielectricsubstrate, but the side of the foil treated in accordance with thepresent invention is not initially bonded to a dielectric substrate(however, in the case of double treated foil, both sides may eventuallybe bonded to dielectric substrates).

Useful dielectric substrates may be prepared by impregnating woven glassreinforcement materials with partially cured epoxy resins (e.g.,difunctional, tetrafunctional and multifunctional epoxies), polyimideresins, or polyester resins. These dielectric substrates are sometimesreferred to as prepregs, such as epoxy prepregs.

In preparing the laminates, it is useful for both the prepreg materialand the metal foil to be provided in the form of long webs of materialrolled up in rolls. In one embodiment, these long webs of metal foil,metal sheet and prepreg are laminated using a continuous process. Inthis process, a continuous web of the article comprising the metal foilwith the inert silane, titanate or zirconate and the metal sheet,optionally with an adhesion promoting layer adhered thereto, is broughtinto contact with a continuous web of prepreg material under laminatingconditions to form a laminate structure. This laminate structure is thencut into rectangular sheets and the rectangular sheets are then laid-upor assembled in stacks of assemblages.

In the third embodiment in which the metal foils are attached to eachother and surround the metal sheet, the long webs of prepreg materialare first cut into rectangular sheets and then subjected to lamination.In this embodiment square or rectangular articles comprising the metalfoil with inert silane, titanate or zirconate and the metal sheets andsquare or rectangular sheets of the prepreg material are then laid-up orassembled in stacks of assemblages referred to as “books.”

Each assemblage may comprise a prepreg sheet with an article comprisingthe metal foil with inert silane, titanate or zirconate and the metalsheet on either side thereof, and in each instance, the adhesion bondingtreated side (or one of the sides) of the metal foil is positionedadjacent the prepreg. The metal sheet is attached to the side of themetal foil away from the prepreg, i.e., the side which has been treatedwith an inert silane. Thus, the side of the metal foil processed inaccordance with the present invention is facing away from the prepregmaterial. The assemblage may be subjected to conventional laminatingtemperatures and pressures between the plates of laminating presses toprepare laminates comprising sandwiches of a sheet of prepreg betweensheets of metal foil.

The prepregs may consist of a woven glass reinforcement fabricimpregnated with a resin, such as a partially cured two-stage resin inembodiments where an epoxy resin is employed. By application of heat andpressure, the untreated (in accordance with the present invention) sideof the copper foil is pressed tightly against the prepreg and thetemperature to which the assemblage is subjected activates the resin tocause curing, that is crosslinking of the resin, which results in tightbonding of the foil to the prepreg dielectric substrate. Generally, thelaminating operation will involve pressures in the range of from about100 psi to about 1,000 psi, temperatures in the range of from about 150°C. to 250° C. and a laminating cycle of from about 10 minutes to about 3hours. The finished laminate may then be utilized to prepare printedcircuit boards (PCB). In one embodiment, the inert silane, titanate orzirconate compound is removed from the copper surface after lamination.

In one embodiment, the laminate is subjected to a subtractive copperetching process to form electrically conductive lines or an electricallyconductive pattern as part of a process for making a multilayeredcircuit board. The inert silane, titanate or zirconate treatment is nextremoved from the patterned metal. A second bonding treatment may then beconducted on the surface of the etched pattern using the techniquesdiscussed above (e.g., barrier and/or treatment layers applied) and thena second prepreg may be adhered to the etched pattern. The etchedpattern exhibits good dimensional control since tarnish is not presentso does not effect the etching process. The techniques for makingmultilayered circuit boards are well known in the art.

A number of manufacturing methods are available for preparing PCBs fromlaminates. Additionally, there is a myriad of possible end useapplications including radios, televisions, computers, etc., for thePCB's. These methods and end uses are known in the art.

One advantage resulting from the present invention is that the treatedmetal foils including the protective film obtained in accordance withthe invention exhibit high tarnish resistance when used in connectionwith metal sheets during lamination to prepregs. This is because theinventive method provides a protective film of an inert silane, titanateor zirconate on the metal foil which maintains a tarnish barrier duringprocessing of the treated metal foil. Another advantage is that thetreated metal foil exhibits excellent pattern ability when later etchingthe foil.

In embodiments where double treated foil is treated in accordance withthe present invention, or where it is desirable to remove the protectivefilm, the treated metal foil is contacted with a dilute aqueous ororganic acid or base solution.

While not wishing to be bound by any theory, it is believed that theindividual molecules of the inert silane, titanate or zirconate compoundare positioned on the surface of the metal foil so that the reactiveportion, e.g., an alkoxy group, reacts with and/or is adjacent the metalfoil surface while the nonpolar, inert substituent, e.g., hydrocarbyl orfluorocarbon group, is positioned away from the metal foil surface. Thenonpolar nature of the inert silane, titanate or zirconate substituentis believed to help prevent tarnish from forming on the metal foilsurface due to electrolysis, oxidation-reduction, or replacementreactions between the metal foil surface and the facing metal sheetwhich is formed of a different metal by forming a non-reactive surface.In addition, the reactive portions of the inert silane, titanate orzirconate have reacted with and thus “tied up” any reactive sites on thesurface of the metal foil. Thus, it is believed the inert silane acts asan insulator, to insulate the metal foil from the metal sheet, which ismade of a different metal. The inert, non-reactive portions of the inertsilane, titanate or zirconate are believed to form a barrier to preventwater molecules from reaching the surface of the metal foil, thuspreventing formation of an electrochemical cell, or battery, between themetal foil and the metal separator sheet comprising a metal differentfrom that of the metal foil.

While not intending to be limited thereby, the following examplesillustrate various and novel aspects of the present invention. Unlessotherwise indicated, in the following examples, as well as throughoutthe specification and claims, all parts and percentages are by weight,all temperatures are in degrees Celsius, and all pressures areatmospheric. Throughout the specification, the upper and lower limits ofall disclosed ranges may be combined.

EXAMPLE 1

Laminates are made using CAC (copper-aluminum-copper) to compare copperfoil treated with an inert silane according to the present inventionwith copper foil treated with standard stabilization treatments, but notwith the inert silane of the present invention.

All copper foils are treated on both sides with a standard metalstabilization layer, specifically a zinc-chromium alloy having athickness of about 0.001 micron.

In an example of the present invention, 36 sheets of copper foil aretreated on both sides with a 0.5% v/v solution of propyltrimethoxysilanein a mixture of water and alcohol, by spraying each sheet of copper foilwith the solution, followed by squeegeeing, followed by oven drying. Thetreatment with the inert silane produces a protective film having athickness of about 0.001 micron on the surface of the copper foil.

As a comparative example, 74 sheets of copper foil are not treated withthe inert silane of the present invention, but are used to form CACarticles with no protective layer.

CAC articles are prepared by attaching the shiny side of each of two 2oz/ft² copper foils to an aluminum sheet by applying an adhesive aroundthe perimeter of the metal sheet.

The matte side of each copper foil, i.e., the side facing away from thealuminum sheet, is laminated to a Polyclad ATS 140° C. T_(g) epoxyprepreg. The lamination is carried out under standard conditions, suchas a pressure of 250 psi, a temperature of 177° C., for a time of 1hour, followed by cooling to room temperature.

After cooling, the aluminum sheet is removed from each of the newlyformed laminates, and the surface of the copper foil (the treated shinyside) is immediately inspected for the presence of any traces oftarnish.

Of the 74 sheets of the comparative copper foil, 17 (23%) show somedegree of tarnish.

Of the 36 sheets of the exemplary copper foil treated in accordance withthe present invention, none show tarnish.

EXAMPLE 2

Nine silane solutions (6 inert silane solutions in accordance with thepresent invention and 3 comparative silane solutions) are preparedcontaining about 1% v/v of the subject silane compound, water, andethanol as needed to dissolve the silane compounds. The silane compoundsare applied to the shiny side of a 1 oz/ft² copper foil, the matte sideof which had been treated with a mixture of zinc and chromium, bydipping into the silane solution with a dwell time of about 20 seconds,rinsing with water, and then drying for about 1 minute at about 100° C.The control foil does not have any silane compound applied thereto. Theshiny side of each copper foil, after this treatment with theappropriate silane (or with no silane treatment, in the control), isattached to an aluminum sheet by a flexible adhesive, in a mannersimilar to that shown in FIG. 3, i.e., by applying a bead of adhesive tothe perimeter of the aluminum sheet and applying the treated copper foilthereto. The matte side of each copper foil, i.e., the side facing awayfrom the aluminum sheet, is then laminated to an epoxy prepreg layer (aPolyclad ATS 140° C. T_(g) epoxy prepreg or a General Electric TS epoxyprepreg). The matte sides of the copper foils are laminated to the epoxyprepreg under standard conditions, such as at 250 psi pressure, at about177° C., and are held together for about 1 hour, followed by cooling toroom temperature.

After cooling, the aluminum sheet is removed from each of the newlyformed laminates, and the surface of the copper foil (the shiny side) isimmediately inspected for the presence of any traces of tarnish. Table 1shows the result, i.e., whether tarnish is observed on the shiny side ofthe copper foils, after the copper foils are separated from theattachment to the aluminum sheet. In classifying the observed degree oftarnish, “heavy” tarnish means that a significant amount of tarnish,i.e., more than a minor amount of discoloration characteristic of aninitial tarnishing, is observed on the copper foil; “some” tarnish meansthat a minor amount of the discoloration characteristic of the initialtarnish is observed on some areas of the copper foils; and “none” meansthat the copper foil appears in substantially pristine condition with noevidence of tarnish formation observable. In each example, the silanecompounds are trimethoxysilanes with the fourth silicon substituentspecified in Table 1.

TABLE 1 Silane Tarnish control Heavy methyl None propyl None isobutylNone octyl None trifluoropropyl None phenyl None aminopropyl Somehydroxypropyl Some glycidoxypropyl Some

As shown by the foregoing results, when an inert silane is applied tothe shiny side of a metal foil, and the shiny side is thereafterattached to a metal sheet of a metal different from the metal foil, andthe article thus formed is laminated to a prepreg, the inert silaneprotects the shiny side of the metal foil from tarnish. A foil which isnot treated an inert silane, titanate or zirconate and so lacks theprotective film becomes tarnished. A foil which is treated withnon-inert silanes is not protected from tarnish, and suffers sometarnish, as shown in the foregoing Table 1. In Table 1, the foilstreated with a non-inert silane and the foil treated with no silane showtarnish after a short storage and lamination under standard prepreglaminating conditions. In contrast, the foils treated with an inertsilane in accordance with the present invention, did not show tarnishafter a short storage and lamination under standard prepreg laminatingconditions.

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various methods thereof willbecome apparent to those skilled in the art upon reading thisspecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications falling withinthe scope of the appended claims.

What is claimed is:
 1. A method of increasing tarnish resistance of ametal foil of a first metal attached or held adjacent to a metal sheetof a second metal, comprising: contacting at least one side of the metalfoil with an inert silane, titanate or zirconate compound to form aprotective film having a thickness from about 0.001 microns to about 1micron on a surface of the metal foil; and attaching or holding adjacentat least a portion of the metal foil having the protective film to themetal sheet.
 2. The method of claim 1, wherein the inert silane compoundcomprises at least one hydrocarbyl silane.
 3. The method of claim 1,wherein the inert silane compound comprises at least onefluorocarbonsilane.
 4. The method of claim 1, wherein the inert silanecompound comprises at least one of methyltrimethoxysilane;ethyltrimethoxysilane; propyltrimethoxysilane; n-butyltrimethoxysilane;isobutyltrimethoxysilane; pentyltrimethoxysilane; hexyltrimethoxysilane;octyltrimethoxysilane; 7-oct-1-enyltrimethoxysilane;phenyltrimethoxysilane; p-(methyl)phenyltrimethoxysilane;3-cyclopentadienylpropyl trimethoxysilane; vinyl trimethoxysilane; allyltrimethoxysilane; methoxypropyl trimethoxysilane; methyltriethoxysilane; ethyl triethoxysilane; propyl triethoxysilane; n-butyltriethoxysilane; isobutyl triethoxysilane; pentyltriethoxysilane;hexyltriethoxysilane; octyltriethoxysilane; 7-oct-1-enyltriethoxysilane; phenyl triethoxysilane; p-(methyl)phenyltriethoxysilane; 3-cyclopentadienylpropyl triethoxysilane; vinyltriethoxysilane; allyl triethoxysilane; methoxypropyl triethoxysilane;methyl triisopropoxysilane; ethyl triisopropoxysilane; propyltriisopropoxysilane; vinyl triisopropoxysilane; vinyltris-t-butoxysilane; 3,3,3-trifluoropropyl trimethoxysilane; andtridecafluoroctyl triethoxysilane.
 5. The method of claim 1, wherein theinert silane compound comprises at least one alkyl silane.
 6. The methodof claim 1, wherein the inert silane compound comprises at least twoinert silane compounds.
 7. The method of claim 1, wherein said titanatecompound is selected from the group consisting of di(cumyl)phenyloxoethylene titanate; di(dioctyl)pyrophosphate oxoethylene titanate;isopropyl triisostearoyl titanate; isopropyl dimethacryl isostearoyltitanate; isopropyl tri(dodecyl)benzenesulfonyl titanate; isopropyltri(dioctyl)phosphato titanate; isopropyl (4-amino)benzenesulfonyldi(dodecyl)benzenesulfonyl titanate; isopropyl tri(dioctyl)pyrophosphatotitanate; tetraoctyl di(ditridecyl)phosphito titanate; tetra (2,2diallyoxymethyl)butyl, di(ditridecyl)phosphito titanate;neopentyl(diallyl)oxy,trineodecanonyl titanate;neopentyl(diallyl)oxy-tri(dodecyl)benzene-sulfonyl titanate;neopentyl(diallyl)oxy-tri(dioctyl)phosphato titanate; andneopentyl(diallyl)oxy-tri(dioctyl)pyro-phosphato titanate; and mixturesof two or more thereof.
 8. The method of claim 1, wherein said zirconateis neopentyl(diallyl)oxy-tri(dioctyl)phosphate zirconate.
 9. The methodof claim 1, wherein said metal foil comprises copper.
 10. The method ofclaim 1, wherein said metal sheet comprises aluminum.
 11. The method ofclaim 1, wherein two said metal foils are attached or held adjacent toone metal sheet.
 12. The method of claim 1, further comprising a step oflaminating to a prepreg a side of the metal foil not attached or heldadjacent to the metal sheet.
 13. A method of increasing tarnishresistance of metal foil comprising: contacting the metal foil with aninert silane compound to form a protective film having a thickness fromabout 0.001 microns to about 1 micron on a surface of the metal foil.14. A method of treating metal foil comprising: contacting a first sideof the metal foil with a hydrocarbylsilane solution to form a protectivefilm on a surface of the metal foil, the hydrocarbylsilane solutioncomprising from about 0.01% to about 10% v/v of a hydrocarbylsilane;attaching or holding adjacent the first side to a metal sheet of a metalother than that of the metal foil; and laminating a second side of themetal foil to a prepreg.
 15. The method of claim 14, wherein thehydrocarbylsilane solution further comprises a triazole compound. 16.The method of claim 14, wherein the prepreg comprises at least one of anepoxy resin material, a polyimide resin material and a polyester resinmaterial.
 17. The method of claim 14, wherein said metal foil comprisescopper.
 18. The method of claim 14, wherein said metal sheet comprisesaluminum.
 19. The method of claim 14, wherein two said metal foils areattached or held adjacent to one metal sheet.
 20. A method of making alaminate comprising: contacting a copper foil with a solution comprisingfrom about 0.05% to about 5% v/v of an alkyl silane; attaching orholding adjacent a first side of the copper foil to an aluminum sheet;and laminating the copper foil to an epoxy resin material.
 21. Themethod of claim 20, wherein the alkyl silane comprisespropyltrimethoxysilane.
 22. The method of claim 20, wherein the solutioncomprises a mixture of water and an organic solvent.
 23. The method ofclaim 20, wherein two said copper foils are attached or held adjacent toone aluminum sheet.